The tricks slidably accommodate and guide needles which during their vertical travel, form the stitch loops in cooperation with the sinkers.
The number of tricks is equal to the number of needles which slide in them with reciprocating movement by the effect of raising and lowering cams.
Generally, in hosiery machines the number of tricks and needles is between 200 and 400.
The cylinder is rotated and with it there rotate the needles which, during their reciprocating movement, are fed with yarn. The yarn is fed at angular positions, when the needles reach their highest point of travel, by feed stations. The feed stations consist of one or more yarn guides which are selectively presented to the needle hooks so that the needles seize the yarn from the guides.
To produce hosiery articles, generally only a fraction of the available needles are used at the same time and in the same manner, except for the plain knitwork parts of the hose. During the formation of the plain knitwork, all the needles are operated between their maximum and minimum level, all needles are fed with yarn at each knitting course, and all of the needles are moved in the same manner.
When the machine is not producing plain knitwork, in order to produce other types of knitwork some needles are required to produce stitch loops and therefore be raised to the maximum level at the feed station in order to seize the yarn. Other needles have to be raised to an intermediate level to take up yarn without clearing the previous stitch in order to form a tuck stitch, or have to be raised with a certain delay so that they do not seize the yarn fed in that feed station and therefore do not form new loops with it. In other words a needle selection has to be made. This means that before each feed, means have to be provided for determining how many needles must undergo a certain travel, which and how many other needles must undergo a certain different travel, and which needles undergo no travel.